1. Field of the Invention
The present invention relates to an image sensor unit used in an image reading apparatus such as a copying machine, image scanner, facsimile and so on, and the image reading apparatus using the image sensor unit. In particular, the present invention relates to an image reading apparatus that authenticates a recording medium, such as a bill, security and so on.
2. Description of the Related Art
As this kind of image reading apparatus, for example, an apparatus disclosed in Patent Document 1 is known as an image reading apparatus that, in particular, authenticates a bill, security and so on.
Patent Document 1: Japanese Laid-open Patent Publication No. 2007-194797
However, in the conventional technology disclosed in the aforementioned Patent Document 1, in a state in which an original is not present when performing reflection reading (for example, when there is a gap between bills when reading bills consecutively, or when there is a damaged portion such as a rip or a tear), there are cases in which light beams emitted from a reflection-type light source enter a light guide (horn-shaped light guide) that is disposed on an opposite side to the original and are re-reflected, and thereafter the light beams are emitted again and enter a light receiving element. Further, a similar situation arises when light beams are transmitted through a watermark portion when reading the watermark portion. The stray light (reflection light that is described later) becomes a noise component in the output of the image sensor unit, and a difference between an output signal (signal component) when an original is present and the noise component produced by the stray light decreases, and this leads to problems such as the contrast becoming blurred and a decrease in the accuracy of a read image.